Films of semiconductors of, e.g., silicon or of compounds of the Groups III and V (e.g., gallium arsenide) can be grown in the vapor phase by introducing the gas containing a source material into a reactor from the top and allowing the material to be reacted or decomposed on a substrate held on a heated susceptor. For this purpose, a variety of apparatuses have been proposed that are capable of forming thin semiconductor films by vapor-phase growth. An example of one such prior art apparatuses for vapor-phase growth is shown in FIG. 1. It comprises a barrel type reactor 1 having on its top an inlet 2 through which the gas containing a source material is introduced, and a barrel type susceptor 3 in a generally conical or polygonal pyramid form that is positioned below the inlet 2 and whose diameter increases toward the downstream portion of the reactor 1. This susceptor 3 is supported on a rotatable shaft 6 and consists essentially of an upper rectifying portion 4 and a lower substrate holding portion 5. A plurality of substrates 7 are placed on the inclined surfaces of the holding portion 5. A radiofrequency (RF) induction coil 8 is mounted around the reactor 1 and the susceptor 3 is heated to a predetermined temperature by RF induction heating with this coil 8. The gas containing a source material is introduced into the reactor 1 together with a carrier gas through the inlet 2 on its top and they undergo pyrolysis reaction in the vicinity of the surface of the heated susceptor 3, thereby allowing a thin semiconductor film to be grown on the substrates 7. The unreacted source material is discharged together with the carrier gas through an exhaust port 9.
The present inventors conducted experiments of vapor-phase growth with the above-described barrel type apparatus and found the following: since the diameter of the susceptor increases by a progressively decreasing degree toward the base, the main stream of the gases flowing between the inner surface of the reactor and the outer surface of susceptor would come closer to the reactor wall by the inertia force and the greater part of the source material would be discharged without reacting through the exhaust port, thereby reducing the efficiency of their utilization. The present inventors also found that the main stream of the gases flow inclined to the reactor wall more conspicuously since the expansion of gas flow whose kinematic viscosity would be increased at higher temperatures was larger on the susceptor side than on the reactor wall side, and this led to a greater decrease in the efficiency of utilization of the source material. In addition, the chance of natural convection of occurring in the space between the reactor wall and the susceptor, namely, the formation of an ascending stream along the susceptor surface, was increased, causing nonuniformity in the thickness of growing film, thereby rendering it very difficult to obtain a profile having an abrupt interface.